The present invention relates to fiber-reinforced resin composites and, more particularly, this invention relates to graphite-fiber-polycarbonate resin composites having improved interfacial adhesion between the fiber and the matrix resin.
There is considerable interest in the use of fiber-reinforced resin composites due to their light weight and high strength. Graphite reinforced composites are finding increasing use in aircraft, spacecraft and space structures such as satellites and space stations. Due to the need to conserve fuel, the weight of automobiles is being reduced by increasing the use of plastics including fiber-reinforced plastics.
Thermoplastic polymers have become of particular interest for use in matrix resins in high performance fiber-resin composites for aerospace applications. They possess high impact resistance, high damage tolerance, high specific strength and modulus, fast processing cycles, and can have high thermal resistance. However, one important limiting factor in the use of these materials is their relatively low bond strength to reinforcing fibers, especially graphite fibers of high modulus.
It is well recognized that the fiber-matrix interface and the extent of bonding between matrix and fiber are of considerable importance to the overall properties and behavior of composites. Stress concentrations occur at the interface due to inevitable differences in the coefficients of thermal expansion, moduli, and Poisson ratios at the fiber and matrix resin. These stresses can lead to dewetting or crack formation along the interface, and, as a result, weaken the composite since the interfacial flaws act as stress concentrators. Since the transmission of applied stress between fiber and matrix depends on the integrity and characteristics of the interface or interphase, a considerable amount of work has been done over the years to understand the interface, to control it, and to modify or tailor it.